Neuroendocrine tumors are tumors that derive from neuroectoderm, and include carcinoid tumor, and islet cell tumors. Some other types of cancers can occasionally have neuroendocrine features such as melanoma and prostate cancer. Neuroendocrine (NE) tumors, such as carcinoid, islet cell tumors, medullary thyroid cancer, small cell lung cancer, certain small intestinal cancers, pheochromocytoma, and paraganglioma, frequently metastasize to the liver, and are second only to colorectal carcinoma as the most common source of isolated hepatic metastases (Sippel and Chen, Problems in General Surgery, 2004, 20:125-133; Chen et al., J. Am. Coll. Surg., 1998, 187:88-92; Chen et al., J. Gastrointest. Surg., 1998. 2:151-155; Elias et al., J. Am. Coll. Surg., 1998, 187:487-493). Over 90% of patients with pancreatic carcinoid tumors and 50% of patients with islet cell tumors develop isolated hepatic metastases (Creutzfeldt W., 1996, World J. Surg. 20:126-131; Hiller et al., 1998, Abdom. Imaging 23:188-190; Mavligit et al., 1993, Cancer 72:375-380; Kebebew et al., 2000, Arch. Surg. 135:895-899; Isozaki et al., 1999, Intern. Med. 38:17-21). Patients with untreated, isolated NE liver metastases have less than 30% 5-year survival probability (Siperstein et al., 1990, World J. Surg. 25:693-696; Elias et al., 1998, J. Am. Coll. Surg. 187:487-493).
While surgical resection can be potentially curative, 90% of patients are not candidates for hepatectomy due to the degree of hepatic involvement by NE tumors (Nave et al., 2001, Surgery 129(2):170-175170-1755).
Besides surgery, however, there are no curative treatments for NE tumors and their hepatic metastases. Presently available alternatives to surgery, including chemoembolization, radiofrequency ablation, cryoablation, chemotherapy, and liver transplantation, have limited efficacy (Brown et al., 1999, J. Vasc. Interv. Radiol. 10:397-403; Isozaki et al., 1999, Intern. Med. 38:17-21; Miller et al., 1998, Oncol. Clin. N. Am. 7:863-879; Prvulovich et al., 1998, J. Nucl. Med. 39:1743-1745; Eriksson et al., 1998, Cancer 83:2293-2301; Lehnert T., 1998, Transplantation 66:1307-1312; Zhang et al., 1999, Endocrinology 140:2152-2158).
In general, chemotherapy has had limited success in patients with NE tumors. Multiple chemotherapeutic agents have been assessed alone or in combination for patients with advanced neuroendocrine tumors. The response rate to chemotherapy in metastatic carcinoid tumors has been reported to be no higher than about 20-30%. In endocrine pancreatic tumors, streptozocin combined with doxorubicin has been reported to generate responses in 69% of patients; however, the determination of response in this trial contained methods unacceptable to today's standards (Sippel and Chen, Problems in General Surgery 2004; 20:125-133). Of note, researchers at the Memorial Sloan-Kettering Cancer Center (MSKCC) reported a patient series treated with this regimen with a response rate of only 6% as determined by standard clinical trial criteria. The chemotherapeutic regimens recommended in neuroendocrine tumors are associated with significant toxicities. For example, the toxicities associated with streptozocin/doxorubicin include vomiting (80% of all patients, 20% severe vomiting), leukopenia (57%), renal insufficiency (44%), stomatitis, and diarrhea. Clearly in patients with a potentially indolent disease, reducing the toxicities associated with treatment is of utmost importance. Less toxic, effective therapies for this population of patients are urgently needed.
Furthermore, patients with liver metastases from NE tumors often have debilitating symptoms, such as uncontrollable diarrhea, flushing, skin rashes, and heart failure due to the excessive hormone secretion that characterizes these tumors. Thus, patients with incurable disease frequently have a poor quality of life. Therefore, for the majority of patients with NE and their hepatic metastases, there is a need for the development of other forms of therapy.
The Notch1 Signaling Pathway
Notch1 is a multi-functional transmembrane receptor that plays an important role in cellular differentiation. (Artavanis-Tsakonas S, et al. Science 1999; 284:770-776; Hald J, et al., Developmental Biology 2003; 260:426-437.) Binding of any one of the Notch ligands (Delta1 and Jagged1, for example) to Notch1 results in activation of the Notch1 protein. (Kageyama R, et al., Cell Res 1999; 9:179-188; Jarriault S, et al., Mol Cell Biol 1998; 18:7423-7431.) The activated-form of Notch1 then translocates to the nucleus and transactivates various target genes such as HES-1. (Chen H, et al., Proc Natl Acad Sci USA 1997; 94:5355-5360.)
Although dysregulation of the Notch pathway has been implicated in several neoplasms, the consequences of such dysregulation is highly cell-type specific. In other words, depending on the specific cancer type, it cannot be expected whether inhibition or activation of the Notch1 would be useful as a cancer therapeutic treatment.
For example, Notch1 has been described as a potential tumor suppressor gene in several cellular contexts. Activation of the Notch1 signaling pathway has been shown to inhibit growth and induce apoptosis in B-cells and other hematopoietc lineages in vitro. (Morimura T, et al., J Biol Chem 2000; 275:36523-36531.) Recently, Notch1 has been reported to function as a tumor suppressor in the skin. (Rangarajan A, et al., Embo Journal 2001; 20:3427-3436; Nicolas M, et al., Nature Genetics 2003; 33:416-421.) In a mouse model of basal cell carcinoma, conditional deletion of Notch1 led to an increase in the number and aggressiveness of skin carcinomas. Notch1 signaling also has been shown to inhibit growth of human hepatocellular carcinoma cells in vitro. (Qi R Z, et al., Cancer Research 2003; 63:8323-8329.) Moreover, transient expression of activated Notch1 by recombinant adenoviruses in small cell lung cancer cell lines has been shown to cause a profound growth arrest. (Sriuranpong V, et al., Cancer Research 2001; 61:3200-3205.) Therefore, these in vitro data suggest that activation of the Notch1 signaling pathway may be a potential therapeutic target for neuroendocrine (NE) tumors.
On the other hand, the constitutively activated form of Notch acts as a bona fide oncogene in leukemia and in murine breast cancer.
Nakakura et al., J. Clin. Endocrinol. Metab. 2005, 90:4350-4356) disclosed that endogenous Notch1 levels in a gastrointestinal (GI) carcinoid cell line (BON cells) was not readily detectable, but infection of the cells with an adenovirus expressing activated Notch1 resulted in accumulation of Notch protein, inhibited general NE marker expression and serotonin production, and inhibited BON cell growth.
Stockhausen et al., 2005, Brit. J. Cancer 92:751-759, discloses that in neuroblastoma (NB) cells, valproic acid (VPA) led to an activated Notch signaling cascade as shown by increased levels of intracellular Notch-1 and Hes-1, and that stimulation of NB cells with VPA led to increased cell death and phenotypic changes associated with differentiation.
However, to date, the ability of Notch1 to suppress gastrointestinal (GI) NE tumor growth has not been explored. In particular, there has been no teaching or suggestion that endogenous Notch1 signaling pathway, or components thereof, can be activated as a treatment or palliative methods for NE tumors. Although Nakakura et al. may appear to suggest that exogenous Notch1 gene may be used for treating NE tumors via gene therapy, there are many shortcomings with this approach. For examples, (1) the therapeutic DNA may be integrated in the host genome and cause mutations which may be oncogenic or otherwise deleterious; (2) the immune system of the patient will react to exogenous genes and their products, reducing the effectiveness of gene therapy, and making it difficult for gene therapy to be repeated in patients; (3) there are a number problems with viral vectors used in gene therapy, such as toxicity, immune and inflammatory responses, and gene control and targeting issues, and the possibility that the viral vector, once inside the patient, may recover its ability to cause disease.